High strength ultra-high molecular weight polyethylene tape articles

ABSTRACT

Processes for the production of high strength polyethylene tape articles from high strength ultra-high molecular weight multi-filament yarns, and to the tape articles, fabrics, laminates and impact resistant materials made therefrom.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of co-pending U.S. application Ser. No.13/494,641, filed Jun. 12, 2012, now U.S. Pat. No. 8,685,519, which is aDivision of U.S. application Ser. No. 12/539,185, filed on Aug. 11,2009, now U.S. Pat. No. 8,236,119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to processes for the production of high strengthpolyethylene tape articles from high strength ultra-high molecularweight multi-filament yarns, and to the tape articles, fabrics,laminates and impact resistant materials made therefrom.

2. Description of the Related Art

Impact resistant and penetration resistant materials find uses in manyapplications such as sports equipment, safety garments, and mostcritically, in personal body armor. The construction of body armor forpersonal protection is an ancient but not archaic art. Metal armor,already well known to the Egyptians by 1500 B.C., persisted in use untilabout the end of the 17^(th) century. In the current era, body armor hasagain become practical through the discovery of new strong fibers suchas aramids, ultra-high molecular weight polyethylene (UHMW PE), andpolybenzazoles.

Various fiber-reinforced constructions are known for use inimpact-resistant, ballistic-resistant and penetration-resistant articlessuch as helmets, panels, and vests. These articles display varyingdegrees of resistance to penetration by impact from projectiles orknives, and have varying degrees of effectiveness per unit of weight. Ameasure of the ballistic-resistance efficiency is the energy removedfrom a projectile per unit of the target's areal density. This is knownas the Specific Energy Absorption, abbreviated as “SEA”, and havingunits of Joules per Kg/m² or J-m²/Kg.

The SEA of a fibrous construction is known to generally increase withincreasing strength, tensile modulus and energy-to-break of theconstituent fibers. However, other factors, such as the shape of thefibrous reinforcement, may come into play. U.S. Pat. No. 4,623,574,presents a comparison between the ballistic effectiveness of a compositeconstructed with a ribbon-shaped reinforcement versus one using amulti-filament yarn: both of UHMW PE. The fiber had a higher tenacitythan the ribbon: 30 grams/denier (abbreviated g/d) versus 23.6 g/d.Nevertheless, the SEA of the composite constructed with the ribbon wassomewhat higher than the SEA of the composite constructed with the yarn.U.S. Pat. No. 4,623,574 teaches that elastomer coated strip or ribboncan be more effective than coated-filament yarn in producing ballisticresistant composites.

The preparation of UHMW PE articles having flat cross-sections by aprocess commonly known as “gel spinning” is described in U.S. Pat. No.4,413,110. A ribbon prepared by the method of U.S. Pat. No. 4,413,110 isdescribed in U.S. Pat. No. 4,623,574. It had a width of 0.64 cm, adenier of 1240, and a tenacity of 23.9 g/d (corresponding to a tensilestrength of 2.04 GPa).

Other processes for the preparation of UHMW PE tape articles aredescribed in U.S. Pat. Nos. 4,996,011; 5,002,714; 5,091,133; 5,106,555,5,200,129; 5,578,373; 5,628,946; 6,017,834; 6,328,923 B1; 6,458,727B1;7,279,441 B2; 6,951,685 B1; U.S. Pat. No. 7,470,459 B1; United StatesPatent Publications 2008/0251960 A1; 2008/0318016 A1; and WO 2009/056286A1.

In one group of these patents, polyethylene filaments were subjected toa contact pressure at elevated temperature to selectively melt a portionof the fibers to bind the filaments together, followed by compression ofthe bound fibers. An UHMW PE SPECTRA® yarn subjected to this process inU.S. Pat. No. 5,628,946 lost 69% of its longitudinal modulus.

In another group of these patents, polyethylene powder was compressed atelevated temperature to bond the particles into a continuous sheet thatwas further compressed and stretched. U.S. Pat. No. 5,091,133 describesa fiber made by this latter process having a tensile strength of 3.4GPa. Polyethylene tapes so produced are commercially available under thetrademark TENSYLON®. The highest tenacity reported on the TENSYLON® website is 19.5 g/d (tensile strength of 1.67 GPa).

Research publications describing preparation of polyethylene tapesand/or flattening of UHMW PE fibers include the following:

R. J. Van et al., “The Hot Compaction of SPECTRA Gel-Spun PolyethyleneFibre”, J. Matl. Sci., 32, 4821-4831 (1997)

A. Kaito et al., “Hot Rolling and Quench Rolling of Ultrahigh MolecularWeight Polyethylene”, J. Appl. Poly Sci., 29, 1207-1220 (1983);“Preparation of High Modulus Polyethylene Sheet by the Roller-DrawingMethod”, J. Appl. Poly Sci., 30, 1241-1255 (1985); “Roller Drawing ofUltrahigh Molecular Weight Polyethylene”, J. Appl. Poly. Sci., 30,4591-4608 (1985)

The highest breaking strength reported in these publications wasapproximately 0.65 GPa corresponding to a tenacity of about 7.6 g/d. Inthe publication by Van et al. cited above, the longitudinal modulus ofthe UHMW PE was reduced by 27 to 74%.

Each of the patents and publications cited above represents improvementin the state of the art. However, none describes the specific process ofthis invention and none satisfies all of the needs met by thisinvention. There is a continuing need for materials that providesuperior resistance to penetration by ballistic projectiles.

As noted above, the SEA of a fibrous construction is known to generallyincrease with increasing strength, tensile modulus and energy-to-breakof the constituent fibers. Highly oriented UHMW PE multi-filament yarnshaving strengths much greater than those of the tape articles of theprior art are commercially available. Conversion of such high strengthyarns into tape articles with substantial retention of strength could behelpful. It could also be helpful to provide woven and non-woven fabricsand ballistic and penetration resistant articles comprising said tapearticles.

SUMMARY OF THE INVENTION

For the purposes of the invention, a polyethylene tape article isdefined as a polyethylene article having a length greater than itswidth, less than about 0.5 millimeter thickness, and having a averagecross-sectional aspect ratio greater than about 10:1.

In one embodiment, the invention is a process for the production of apolyethylene tape article of indefinite length comprising:

-   -   a) selecting at least one polyethylene multi-filament yarn, said        yarn having a c-axis orientation function at least 0.96, an        intrinsic viscosity when measured in decalin at 135° C. by ASTM        D1601-99 of from about 7 dl/g to 40 dl/g, and said yarn having a        tenacity of from about 15 g/d to about 100 g/d as measured by        ASTM D2256-02 at a 10 inch (25.4 cm) gauge length and at an        extension rate of 100%/min;    -   b) placing said yarn under a longitudinal tensile force and        subjecting said yarn to at least one transverse compression step        to flatten, consolidate and compress said yarn at a temperature        of from about 25° C. to about 137° C., thereby forming a tape        article having a average cross-sectional aspect ratio at least        about 10:1, each said compression step having an outset and a        conclusion wherein the magnitude of said longitudinal tensile        force on each said yarn or tape article at the outset of each        said compression step is substantially equal to the magnitude of        the longitudinal tensile force on the yarn or tape article at        the conclusion of that same compression step, and is at least        about 0.25 kilogram-force (2.45 Newtons).    -   c) stretching said tape article at least once at a temperature        in the range of from about 130° C. to about 160° C. at a stretch        rate of from about 0.001 min⁻¹ to about 1 min⁻¹;    -   d) optionally repeating step b) one or more times at a        temperature from about 100° C. to about 160° C.;    -   e) optionally repeating step c) one or more times;    -   f) optionally relaxing the longitudinal tensile force between        any of steps b) to e);    -   g) optionally increasing the longitudinal tensile force between        any of steps b) to e)    -   h) cooling said tape article to a temperature less than about        70° C. under tension.

In a second embodiment, the invention is a process for the production ofa polyethylene tape article of indefinite length comprising:

-   -   a) selecting at least one polyethylene multi-filament yarn, said        yarn having a c-axis orientation function at least 0.96, an        intrinsic viscosity when measured in decalin at 135° C. by ASTM        D1601-99 of from about 7 dl/g to 40 dl/g, said yarn having a        tenacity of from about 15 g/d to about 100 g/d as measured by        ASTM D2256-02 at a 10 inch (25.4 cm) gauge length and at an        extension rate of 100%/min;    -   b) passing said yarn through one or more heated zones at        temperatures of from about 100° C. to about 160° C. under        tension;    -   c) stretching said heated yarn at least once at a stretch rate        of from about 0.01 min⁻¹ to about 5 min⁻¹.    -   d) placing said yarn under a longitudinal tensile force and        subjecting said yarn to at least one transverse compression step        to flatten, consolidate and compress said yarn at a temperature        of from about 100° C. to about 160° C., thereby forming a tape        article having a average cross-sectional aspect ratio at least        about 10:1, each said compression step having an outset and a        conclusion wherein the magnitude of said longitudinal tensile        force on each said yarn or tape article at the outset of each        said compression step is substantially equal to the magnitude of        the longitudinal tensile force on the yarn or tape article at        the conclusion of that same compression step, and is at least        about 0.25 kilogram-force (2.45 Newtons).    -   e) stretching said tape article at least once at a temperature        of from about 130° C. to about 160° C. at a stretch rate of from        about 0.001 min⁻¹ to about 1 min⁻¹;    -   f) optionally repeating step d) one or more times;    -   g) optionally repeating step e) one or more times;    -   h) optionally relaxing the longitudinal tensile force between        any of steps c) to g)    -   i) optionally increasing the longitudinal tensile force between        any of steps c) to g)    -   j) cooling said tape article to a temperature less than about        70° C.;

In a third embodiment, the invention is a polyethylene tape article ofindefinite length and an average cross-sectional aspect ratio at least10:1, said polyethylene having an intrinsic viscosity when measured indecalin at 135° C. by ASTM D1601-99 of from about 7 dl/g to about 40dl/g, and when measured by ASTM D882 at a 10 inch (25.4 cm) gauge lengthand at an extension rate of 100%/min, said tape article having a tensilestrength at least about 3.6 GPa.

In a fourth embodiment, the invention is a fabric comprising tapearticles of the invention, said fabric being selected from the groupconsisting of woven, knitted and three dimensionally woven.

In a fifth embodiment, the invention is a laminate comprising two ormore unidirectional layers of the tape articles of the invention withthe tape direction in adjoining layers being rotated from each other byfrom about 15 to about 90 degrees.

In a sixth embodiment, the invention is an impact and penetrationresistant composite comprising at least one member selected from thegroup consisting of a fabric of the invention, a laminate of theinvention, and their combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first apparatus for implementing a process of theinvention.

FIG. 2 illustrates a second apparatus for implementing a process of theinvention.

FIG. 3 illustrates a third apparatus for implementing a process of theinvention.

FIG. 4 illustrates a fourth apparatus for implementing a process of theinvention.

FIG. 5 illustrates a fifth apparatus for implementing a process of theinvention.

FIG. 6 illustrates a sixth apparatus for implementing a process of theinvention.

FIG. 7 illustrates a seventh apparatus for implementing a process of theinvention.

In each figure only one yarn end is shown for clarity. It will beunderstood that several yarn ends may be simultaneously treated inparallel by a process of the invention to produce several parallel tapearticles, or a single wide tape article.

DETAILED DESCRIPTION OF THE INVENTION

We provide a process for converting high strength UHMW PE yarns intotape articles with substantial retention of strength. The inventivemethod provides substantially equal longitudinal tensile forces across acompression step. It is believed the inventive method is superior toprior art methods that maintain equal tensile stress (g/d) across acompression step with consequent unbalanced tensile forces.

For the purposes of the invention, a polyethylene tape article isdefined as a polyethylene article having a length greater than itswidth, less than about 0.5 millimeter thickness, and having a averagecross-sectional aspect ratio greater than about 10:1. Preferably, a tapearticle of the invention has a width less than about 100 cm, morepreferably less than about 50 cm, yet more preferably less than about 25cm, and most preferably, less than about 15.2 cm.

Preferably a tape article of the invention has a thickness less thanabout 0.25 millimeter, more preferably, a thickness less than about 0.1millimeter, and most preferably, a thickness less than 0.05 millimeter.Thickness is measured at the thickest region of the cross-section.

Average cross-sectional aspect ratio is the ratio of the greatest to thesmallest dimension of cross-sections averaged over the length of thetape article. Preferably, a tape article of the invention has an averagecross-sectional aspect ratio at least about 20:1, more preferably atleast about 50:1, yet more preferably at least about 100:1, still morepreferably at least about 250:1 and most preferably, at least about400:1.

The cross-section of a tape article of the invention may be rectangular,oval, polygonal, irregular, or of any shape satisfying width, thicknessand aspect ratio requirements. Preferably, a tape article of theinvention has an essentially rectangular cross-section.

The UHMW PE yarn selected as a feed for a process of this invention maybe prepared by any convenient method. Preferably, the selected UHMW PEyarn is prepared by “gel spinning”. Gel spun UHMW PE yarns arecommercially available from Honeywell International under the tradenameSPECTRA®, from DSM N.V. and Toyobo Co. Ltd. Under the trade nameDYNEEMA®, from Shanghai Pegaus Materials Co., Ltd., from Hangzhou HighStrength Fiber Material Inc. and from others.

The UHMW PE yarn selected as a feed for a process of this invention hasa intrinsic viscosity when measured in decalin at 135° C. by ASTMD1601-99 of from about 7 dl/g to about 40 dl/g, preferably from about 10dl/g to about 40 dl/g, more preferably from about 12 dl/g to about 40dl/g, and most preferably, from about 14 dl/g to 35 dl/g.

The UHMW PE yarn selected as a feed for a process of this invention ishighly oriented. A highly oriented UHMW PE yarn in the context of theinvention is defined as having a c-axis orientation function at leastabout 0.96, preferably at least about 0.97, more preferably at leastabout 0.98 and most preferably, at least about 0.99. The c-axisorientation function is a description of the degree of alignment of themolecular chain direction with the fiber direction and is calculatedfrom the equation reported by R. S. Stein, J. Poly Sci., 31, 327 (1958).

$f_{c} = {\frac{1}{2}\left( {{3\left\langle {\cos\;\theta} \right\rangle^{2}} - 1} \right)}$where θ is the angle between the c-axis of the polyethylene crystals(the molecular chain direction) and the fiber direction and the caretsindicate the average of the quantity therebetween.

The average cosine of the angle between the “c” crystal axis and thefiber direction is measured by well known x-ray diffraction methods. Apolyethylene fiber in which the molecular chain direction is perfectlyaligned with the fiber axis would have a f_(c)=1.

The UHMW PE yarn selected as a feed for a process of this invention hasa tenacity from about 15 g/d to about 100 g/d, preferably from about 25g/d to about 100 g/d, more preferably from about 30 g/d to about 100g/d, yet more preferably from about 35 g/d to about 100 g/d, still morepreferably from about 40 g/d to about 100 g/d and most preferably, fromabout 45 g/d to about 100 g/d.

The UHMW PE yarn selected as a feed for a process of this invention maybe untwisted or it may be twisted. Preferably the yarn has less thanabout 10 turns of twist per inch of length. The UHMW PE yarn selected asa feed may be heat set by a process described in U.S. Pat. No. 4,819,458hereby incorporated by reference to the extent not incompatibleherewith.

The UHMW PE yarn selected as a feed for a process of this invention mayconsist of unconnected filaments, or the filaments may be at leastpartially connected by fusion or by bonding. Fusion of UHMW PE yarnfilaments may be accomplished by various means. Convenient means includethe use of heat and tension, or through application of a solvent orplasticizing material prior to exposure to heat and tension as describedin U.S. Pat. Nos. 5,540,990, 5,749214, 6,148,597 hereby incorporated byreference to the extent not incompatible herewith. Bonding may beaccomplished by at least partially coating the filaments with a materialhaving adhesive properties, such as KRATON® D1107.

In a first embodiment, the invention is a process for the production ofa polyethylene tape article of indefinite length comprising:

-   -   a) selecting at least one polyethylene multi-filament yarn, said        yarn having a c-axis orientation function at least 0.96, an        intrinsic viscosity when measured in decalin at 135° C. by ASTM        D1601-99 of from about 7 dl/g to 40 dl/g, and said yarn having a        tenacity of from about 15 g/d to about 100 g/d as measured by        ASTM D2256-02 at a 10 inch (25.4 cm) gauge length and at an        extension rate of 100%/min;    -   b) placing said yarn under a longitudinal tensile force and        subjecting said yarn to at least one transverse compression step        to flatten, consolidate and compress said yarn at a temperature        of from about 25° C. to about 137° C., thereby forming a tape        article having a average cross-sectional aspect ratio at least        about 10:1, each said compression step having an outset and a        conclusion wherein the magnitude of said longitudinal tensile        force on each said yarn or tape article at the outset of each        said compression step is substantially equal to the magnitude of        the longitudinal tensile force on the yarn or tape article at        the conclusion of that same compression step, and is at least        about 0.25 kilogram-force (2.45 Newtons).    -   c) stretching said tape article in at least one stage at a        temperature in the range of from about 130° C. to about 160° C.        at a stretch rate of from about 0.001 min⁻¹ to about 1 min⁻¹;    -   d) optionally repeating step b) one or more times at a        temperature from about 100° C. to about 160° C.;    -   e) optionally repeating step c) one or more times;    -   f) optionally relaxing the longitudinal tensile force between        any of steps b) to e);    -   g) optionally increasing the longitudinal tensile force between        any of steps b) to e);    -   h) cooling said tape article to a temperature less than about        70° C. under tension.

Preferably, steps b) through h) are performed continuously.

In a second embodiment, the invention is a process for the continuousproduction of a polyethylene tape article of indefinite lengthcomprising:

-   -   a) selecting at least one polyethylene multi-filament yarn, said        yarn having a c-axis orientation function at least 0.96, an        intrinsic viscosity when measured in decalin at 135° C. by ASTM        D1601-99 of from about 7 dl/g to 40 dl/g, said yarn having a        tenacity of from about 15 g/d to about 100 g/d as measured by        ASTM D2256-02 at a 10 inch (25.4 cm) gauge length and at an        extension rate of 100%/min;    -   b) passing said yarn continuously through one or more heated        zones at temperatures of from about 100° C. to about 160° C.        under tension;    -   c) stretching said heated yarn at least once at a stretch rate        of from about 0.01 min⁻¹ to about 5 min⁻¹.    -   d) placing said yarn under a longitudinal tensile force and        subjecting said yarn to at least one transverse compression step        to flatten, consolidate and compress said yarn at a temperature        of from about 100° C. to about 160° C., thereby forming a tape        article having a average cross-sectional aspect ratio at least        about 10:1, each said compression step having an outset and a        conclusion wherein the magnitude of said longitudinal tensile        force on each said yarn or tape article at the outset of each        said compression step is substantially equal to the magnitude of        the longitudinal tensile force on the yarn or tape article at        the conclusion of that same compression step, and is at least        about 0.25 kilogram-force (2.45 Newtons).    -   e) stretching said tape article at least once at a temperature        of from about 130° C. to about 160° C. at a stretch rate of from        about 0.001 min⁻¹ to about 1 min⁻¹;    -   f) optionally repeating step d) one or more times;    -   g) optionally repeating step e) one or more times;    -   h) optionally relaxing the longitudinal tensile force between        any of steps c) to g);    -   i) optionally increasing the longitudinal tensile force between        any of steps c) to g)    -   j) cooling said tape article to a temperature less than about        70° C. under tension;

Preferably, steps b) through j) are performed continuously.

A continuous process of the first embodiment is illustratedschematically in FIGS. 1, 2 and 7. A continuous process of the secondembodiment is illustrated schematically in FIGS. 3-6. The figuresillustrating a particular embodiment differ in the number and placementof process equipment, but illustrate the same steps.

In each of FIGS. 1 to 7 a selected multi-filament UHMW PE yarn (10-16respectively) is unwound from a package or beam (not shown) and ispassed over and under several restraining rolls (20). The restrainingrolls are at temperature of from about 25° C. to about 137° C.

In FIGS. 1-2 and 7, the yarn leaving the restraining rolls (80, 81, 86respectively) is passed under tension directly into one or more means(30, 33, 39) for compressing, consolidating, and flattening the yarn,thereby forming a tape article. The tape article is subsequently heatedand stretched at least once.

In FIGS. 3 to 6 the yarn leaving the restraining rolls (82-85respectively) is heated and stretched before reaching a means forcompression. Heating of a yarn may be by any means, such as by infra-redradiation, contact with a heated surface, or contact with a heatedfluid. Preferably, the yarn is heated and stretched in a forcedconvection air oven (50-59, 510 in FIGS. 1-7) having multipletemperature zones. The yarn is stretched at least once at temperaturesof from about 100° C. to about 160° C. at a stretch rate of from about0.01 min⁻¹ to about 5 min⁻¹. Stretch rate is defined as the differencebetween the speed at which a material leaves a stretch zone (V₂) and thespeed at which it entered a stretch zone (V₁) divided by the length ofthe stretch zone (L), i.e.,Stretch rate=(V2−V1)/L, min⁻¹

Preferably, the yarn is stretched to a stretch ratio of from about1.01:1 to about 20:1 at a temperature of about 135° C. to about 155° C.Preferably, the stretch ratio is the maximum possible without rupturingthe yarn.

In both of the above embodiments, each yarn or tape article is under alongitudinal tensile force at both the outset and conclusion ofcompression in each means for compression (30-40). Longitudinal tensileforce is regulated by regulating the speeds of successive driven means.

The magnitude of the longitudinal tensile force on the yarn or tapearticle at the outset of each compression step is substantially equal tothe magnitude of the longitudinal tensile force on the yarn or tapearticle at the conclusion of the same compression step. In the contextof the invention, the term “substantially equal” means that the ratio ofa lower to higher tensile force across a compression step is at least0.75:1, preferably at least 0.80:1, more preferably at least 0.85:1, yetmore preferably, at least 0.90:1, and most preferably, at least 0.95:1.Such substantially equal longitudinal tensile force at the outset andconclusion of a compression step is a fundamental feature of theinventive process. Equal tensile forces across a compression stepassures zero tension at the midpoint of compression.

It is believed the inventive method is superior to prior art methodsthat maintain equal tensile stress (g/d) across a compression means withconsequent unbalanced tensile forces as denier is reduced. The inventivemethod enables higher pressures and higher temperatures in a compressionstep without rupture of the yarn or tape article or slippage in a meansfor compression. It is believed that this enables higher productionsspeeds and ability to achieve superior strengths.

The longitudinal tensile force is at least 0.25 kilogram-force(abbreviated Kgf, equal to 2.45 Newtons, abbreviated N) on the yarn ortape article at the inlet and at the outlet of a compression step.Preferably, the tensile force is at least 0.5 Kgf (4.9 N), morepreferably at least 1 Kgf (9.8 N), yet more preferably at least 2 Kgf(19.6.2 N), and most preferably, at least 4 Kgf (39.2 N) at the outsetand conclusion of a compression step. Most preferably, longitudinaltensile force is as high as possible without rupturing the yarn or tapearticle and without causing slippage of the yarn or tape article in acompression means.

For the sake of definiteness without intending to limit the scope of theinvention, the illustrated compression means (30-40) in each of FIGS.1-7 are counter-rotating, opposed rolls (nip rolls): each nip roll of aunit preferably has the same surface speed, and presses upon the yarn ortape article. Other suitable and well known compression means includenip roll stacks consisting of three or more rolls in a single unit thatprovide two or more compressions, pairs of moving belts that press fromopposite sides against the yarn or tape article, rolls where the yarn ortape article makes a 180° turn under high tension and the like. Thepressure applied by nip rolls and moving belts may be actuated byhydraulic cylinders, or the pressure may result from fixing a gapbetween the rolls at a dimension smaller than the thickness of theincoming material. Still other compression means are possible and arecontemplated.

The means for compression may be vibrated. Considering the tape articleto be a quasi-two dimensional object with length and width butnegligible thickness, the vibration may be in a direction normal to theplane of the tape article, or in the plane of the tape article or in adirection inclined to both planes. The vibration may be of lowfrequency, or of sonic or ultra-sonic frequencies. The vibration may beused as an aid in consolidation by imparting additional pulses ofpressure or shear. It may also be used to produce periodic variations inthickness or width of the compressed article useful for bonding incomposite applications.

The pressure exerted in a compression step in each embodiment is fromabout 20 to about 10,000 pounds per square inch (psi) (about 0.14 toabout 69 MPa), preferably from about 50 to about 5000 psi (about 0.34 toabout 34 MPa), and more preferably from about 50 to about 2500 psi(about 0.69 to about 17 MPa). The pressure is preferably increased atsuccessive stages of compression. The compression means are at atemperature of from about 25° C. to about 160° C., preferably from about50° C. to about 155° C., and more preferably from about 100° C. to about150° C.

After passage through at least one compression means, e.g. (30) in FIG.1, a now formed tape article (100) is heated and stretched at leastonce. Heating of the tape article may be by any means, such as byinfra-red radiation, contact with a heated surface, or contact with aheated fluid. Preferably, the tape article is heated and stretched in aforced convection air oven (50, 51) having multiple temperature zonesdemarcated by the dashed lines in the figures. Not shown in the figuresare heaters and blowers to heat and circulate the air through the oven.

Stretching of the tape article is at a temperature of from about 100° C.to about 160° C., and preferably from about 135° C. to about 150° C. Thetape article is stretched at a stretch rate of from about 0.001 min⁻¹about 1 min⁻¹. Preferably the tape article is stretched at a stretchrate of from about 0.001 min⁻¹ to about 0.1 min⁻¹. Preferably the tapearticle is stretched to a stretch ratio of from about 1.01:1 to 20:1.

The stretching force may be applied by any convenient means such as bypassing the yarn over and under a sufficient number of driven rolls(60), as illustrated in FIGS. 2, 3, 4 and 6; by compression means (31,32, 40) as illustrated in FIGS. 1 and 7; by both compression means (36,37, 40) and driven rolls (60, 61) as in FIGS. 5 and 7; or by winding thetape article multiple times around a driven godet and idler roll pair(not illustrated). Driven rolls applying the stretching force may beinternal to the oven or outside of the oven.

The longitudinal tensile force need not be the same throughout acontinuous operation. Optionally, a yarn or tape article may be relaxedto lower longitudinal tensile force or permitted to shrink less thanabout 5% between successive compressions or stretches by tensionisolation means. Alternatively, tension may be increased betweensuccessive compressions or stretches by tension isolation means. In FIG.7, rolls (61) act as tension isolation means. The tensile force on tapearticle (114) can be either greater or less than on tape article (113),depending on the speed of nip rolls (39) and (40) and the temperaturesin the two ovens. In either case, the speed of restraining rolls (20)and driven rolls (60) are adjusted to maintain the tensile forceconstant across the compression means (39 and 40).

The tape article is cooled under tension prior to being conveyed to awinder. The length of the tape article will diminish slightly caused bythermal contraction, but tension should be sufficiently high duringcooling to prevent shrinkage beyond thermal contraction. Preferably, thetape article is cooled on rolls (60) and the rolls are cooled by naturalconvection, forced air, or are internally water-cooled. The finalstretched tape article (70-76), cooled under tension to a temperatureless than about 70° C., is wound up under tension (winder not shown) asa package or on a beam.

As noted above, the number and placement of compression and stretchingmeans may be varied within a particular embodiment as is illustratedschematically in the Figures.

FIG. 1 illustrating the first embodiment shows a sequence ofcompression-stretching-compression-stretching-compression.

FIG. 2 illustrating the first embodiment shows a sequence ofcompression-compression-stretching.

FIGS. 3-6 illustrate the second embodiment of the invention. FIG. 3shows a sequence of stretching-compression-stretching.

FIG. 4 shows a sequence of stretching-three consecutivecompressions-stretching.

FIG. 5 shows a sequence ofstretching-compression-stretching-compression-stretching in a six zoneoven (57).

FIG. 6 shows a sequence of stretching-two consecutivecompressions-stretching in a four zone oven (58).

FIG. 7, illustrating the first embodiment, shows a sequence ofcompression-stretching-stretching at increased tensileforce-compression.

Many other processing sequences consistent with one of either the firstor second embodiments of the invention are possible, and arecontemplated.

Preferably, a process of the invention produces a tape article having atensile strength at least about 2.2 GPa, more preferably at least about2.6 GPa, yet more preferably at least about 3.0 GPa, and mostpreferably, at least about 3.6 GPa.

Preferably, a process of the invention produces a tape article having atensile strength at least 75% of the strength of the yarn from which itis made. More preferably, a process of the invention produces a tapehaving a higher tensile strength than the yarn from which it is made.

A third embodiment of the invention is a polyethylene tape article ofindefinite length and an average cross-sectional aspect ratio at least10:1, said polyethylene having an intrinsic viscosity when measured indecalin at 135° C. by ASTM D1601-99 of from about 7 dl/g to about 40dl/g, and when measured by ASTM D882 at a 10 inch (25.4 cm) gauge lengthand at an extension rate of 100%/min, said tape article having a tensilestrength at least about 3.6 GPa.

In a fourth embodiment, the invention is a fabric comprising tapearticles of the invention, said fabric being selected from the groupconsisting of woven, knitted and three dimensionally woven. Preferably,a fabric of the invention is comprised of at least 50% by weight of tapearticles of the invention.

In a fifth embodiment, the invention is a laminate comprising two ormore unidirectional layers of the tape articles of the invention withthe tape direction in adjoining layers being rotated from each other byfrom about 15 to about 90 degrees.

In a sixth embodiment, the invention is an impact and penetrationresistant composite comprising at least one member selected from thegroup consisting of a fabric of the invention, a laminate of theinvention, and their combination. Preferably, a composite of theinvention is resistant to penetration by ballistic projectiles and byknives and other sharp or pointed implements.

The following examples are presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials, proportions and reported data set forth to illustrate theprinciples of the invention are exemplary and should not be construed aslimiting the scope of the invention.

Measurement Methods

Intrinsic Viscosity

Measurements of intrinsic viscosity were made by ASTM D1501-99 indecalin solution at 135° C.

Yarn Tenacity

Yarn tenacity was measured by ASTM D2256-02 at 10 inch (25.4 cm) gaugelength and at an extension rate of 100% min.

Tape Tensile Strength

Tape tensile strength was measured by ASTM D882-09 at 10 inch (25.4 cm)gauge length and at an extension rate of 100%/min.

Orientation Function

C-axis orientation function (f_(c)) was measured by the wide angle x-raydiffraction method described in Correale, S. T. & Murthy, Journal ofApplied Polymer Science, Vol. 101, 447-454 (2006) as applied topolyethylene,

EXAMPLES

Examples 1 to 2 were tests of simplified systems.

Example 1 Comparative

A 1200 denier multi-filament UHMW PE yarn having an intrinsic viscosityof 12 dl/g, a c-axis orientation function of 0.99, and a initialtenacity of 28 g/d was twisted 7 turns/inch (2.76 turns/cm). Tenacity ofthe twisted yarn was 15.5 g/d. The twisted yarn was drawn and fused andthen statically compressed in a press between platens at a temperatureof 22° C. and a pressure of about 8,000 psi (about 55 MPa). The tensilestrength of the tape article was 2.0 GPa corresponding to a tenacity of23.4 g/d. The tape article had retained 83.6% of the strength of theoriginal untwisted yarn.

Example 2 Comparative

A 4800 denier multi-filament UHMW PE yarn having an intrinsic viscosityof 14 dl/g, a c-axis orientation function of 0.99, and a tenacity of 28g/d was twisted about 0.025 turns per inch (about 0.01 turns/cm). Theyarn was stretched at a ratio of 2.5:1 in a forced air convection ovenat a temperature of 155.5° C. and at a stretch rate of 1.07 min⁻¹. Thefilaments of the yarn were thereby at least partially fused together.The tenacity of the stretched and fused yarn was 20 g/d.

The stretched and fused yarn having a diameter of about 0.065 cm wascontinuously pulled along a steel plate at a temperature of 152° C. andthen through a fixed gap between the lower heated plate and an unheatedupper steel plate. The upper plate was inclined at an angle to the lowerplate such that its lower edge defined a line of contact with the yarn.The tensile force on the yarn was 225 g entering the gap and 400 gleaving the gap.

The yarn was continuous flattened, consolidated and compressed onpassing through the gap under tension, thereby forming a tape. The taperemained in contact with the heated plate beyond the compression gap andsome stretching may have occurred.

The tape article thereby produced had lateral dimensions of 0.005 inch(0.0127 cm) thickness by 0.10 inch (0.254 cm) width, and an aspect ratioof 20:1. The tape tensile strength was 1.62 GPa, corresponding to atenacity of 19 g/d and 68% of the strength of the original yarn.

Example 3

The following example sets forth the best mode contemplated by theinventors of carrying out the first embodiment of the invention.

A 1200 denier gel spun multi-filament UHMW PE yarn twisted about 0.01turns/cm is selected having an intrinsic viscosity of 14 dl/g, a c-axisorientation function of 0.99, and a tenacity of 47 g/d.

As illustrated in FIG. 1, the yarn (10) is unwound from a package on acreel (not shown) and is passed over restraining rolls (20). The rollsare at a temperature of 130° C. The yarn leaving the restraining rolls(80) is passed at a speed of 5 meters/min directly into a first pair ofcompression nip rolls (30). The nip rolls apply a longitudinal tensileforce of 2.5 Kgf (24.5 N) to the yarn. The nip rolls are at atemperature of 135° C. The yarn is flattened, consolidated andcompressed in the nip rolls under a pressure of about 500 psi (about 3.4KPa) forming a tape article (100). The tape article leaving the firstpair of nip rolls (30) is under a longitudinal tensile force of 2.5 Kgf(24.5 N) applied by a second pair of nip rolls (31).

The tape article (100) enters and traverses two zones of a forced airconvection oven (50) in passing between nip rolls (30) and (31). Thetemperatures in the oven are: Zone 1-149° C., Zone 2-150° C. The tapearticle (100) is stretched at a stretch rate of 0.11 min⁻¹ in the oven(50). The stretched tape article is compressed a second time in niprolls (31, and is passed into a second oven (51). The second nip rolltemperatures are 147° C.

The twice-compressed and once-stretched tape article (101) is stretchedat a stretch rate of 0.096 min⁻¹ in the first and second zones of thesecond oven (51) under the influence of a longitudinal tensile force of2.5 Kgf (29.4 N) applied by a third pair of nip rolls (32). Zonetemperatures in oven (51) are 151° C. and 152° C. respectively.

The tape article is then compressed a third time under a pressure ofabout 500 psi (about 3.4 KPa) at nip roll temperatures of 150° C. in thethird set of nip rolls (32). The longitudinal tensile force in the tapearticle is essentially constant at 2.5 Kgf (29.4 N) at the inlet and atthe outlet of the third set of nip rolls. The longitudinal tensile forcein the tape article at the outlet of the third set of nip rolls (32) isapplied by external rolls (60).

The tape is cooled under tension to a temperature of 50° C. on theexternal rolls (60). The final tape article (70) is wound up undertension at a speed of 7.5 meters/min.

The novel tape article produced has an essentially rectangularcross-section with a thickness of 0.00697 cm, a width of 0.135 cm and anaverage cross-sectional aspect ratio of 20:1. The tensile strength ofthe tape article is 3.6 GPa corresponding to a tenacity of 42 g/d. Thetape article retains 89% of the strength of the yarn from which it isproduced.

Example 4

The following example sets forth the best mode contemplated by theinventors of carrying out the second embodiment of the invention.

A 4800 denier gel spun multi-filament UHMW PE yarn twisted 0.01 turns/cmis selected having an intrinsic viscosity of 15 dl/g, a c-axisorientation function of 0.98, and a tenacity of 45 g/d.

As illustrated in FIG. 3 the yarn (12) is unwound from a package on acreel (not shown) and is passed continuously over restraining rolls(20). The rolls are at a temperature of 135° C. The yarn leaving therestraining rolls (82) is passed at a speed of 5 meters/min into a twozone oven (53) under a longitudinal tensile force of 8 Kgf (78.4 N). Thelongitudinal tension force is regulated by the speed of the nip rolls(34). The first and second oven zone temperatures are 149° C. and 150°C. respectively. The yarn is stretched at a stretch rate of 0.09 min⁻¹in the oven (53) before entering the nip rolls. The stretched yarn iscompressed in nip rolls (34) at a temperature of 152° C. forming a tapearticle. The tape article is passed into a second oven (54) andstretched under a longitudinal tensile force of 8 Kgf (78.4N). Thelongitudinal tensile force is regulated by the speed of the externalrolls (60). The tape article is stretched at a stretch rate of 0.086min⁻¹ at a temperature of 152° C.

The tape is cooled under tension to a temperature of 50° C. on theexternal rolls (60). The final tape article (72) is wound up undertension at a speed of 7 meters/min.

The novel tape article produced has an essentially rectangularcross-section with a thickness of 0.00627 cm, a width of 0.627 cm and anaverage cross-sectional aspect ratio of 100:1. The tensile strength ofthe tape article is 3.6 GPa corresponding to a tenacity of 42 g/d. Thetape article retains 93% of the strength of the yarn from which it isproduced.

Example 5

A tape article of the invention as described in Example 3 is woven intoa plane weave fabric having a warp and fill count of 7.2 per centimeter.

Example 6

A tape article of the invention as described in Example 4 is woven intoa plane weave fabric having a warp and fill count of 1.5 per centimeter.

Example 7

A tape article of the invention as described in Example 3 or in Example4 is wound up in a multiplicity of packages and the packages are placedon a creel. Multiple ends of the tape articles, unwound from the creel,aligned parallel in lateral contact, are place on a carrier webconsisting of a high density polyethylene (HDPE) film of 0.00035 cmthickness. The carrier web and tape articles are passed through heatednip rolls under pressure to adhere the tape articles to the carrier web.The carrier web and adhering parallel tape articles are wound up in tworolls.

The two rolls are fed into a cross-plying apparatus as described in U.S.Pat. No. 5,173,138 wherein the webs containing the tape articles arecross-plied and consolidated by means of heat and pressure. A four layerlaminate is thereby formed where the layers, in sequential order throughthe laminate are HDPE-tape articles-tape articles-HDPE, and thedirection of the tapes in adjacent layers are at right angles to oneanother. This laminate of the invention is rolled up.

Example 8

Fabrics of the invention as described in Example 5 or Example 6 areplied up and loosely connected to form an assembly of the inventionhaving an areal density of 1.5 Kg/m². It is expected that the assemblyof the invention has a specific energy absorption at least about 500J-m2/Kg against a 9×19 mm FMJ Parabellum bullet as measured by MIL.-STD.662F

Example 9

Laminates of the invention as described in Example 7 are plied up andconsolidated to form an impact and penetration resistant compositearticle of the invention having an areal density of 1.5 Kg/m². It isexpected that the composite article of the invention has a specificenergy absorption at least about 500 J-m2/Kg against a 9×19 mm FMJParabellum bullet as measured by MIL.-STD. 662F

Having thus describe the invention in rather full detail, it will beunderstood that such detail need not be strictly adhered to but thatfurther changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention as defined bythe subjoined claims.

What is claimed is:
 1. A laminate comprising two or more unidirectionallayers of polyethylene tape articles, said polyethylene tape articleshaving an average cross-sectional aspect ratio of at least about 10:1,said polyethylene having an intrinsic viscosity when measured in decalinat 135° C. by ASTM D1601-99 of from about 7 dl/g to 40 dl/g, and whenmeasured by ASTM D882-09 at a 10 inch (25.4 cm) gauge length and at anextension rate of 100%/min, said tape articles having a tensile strengthof at least about 2.2 GPa, with the tape direction in adjoining layersbeing rotated from each other by from about 15 to about 90 degrees.
 2. Afabric comprising polyethylene tape articles, said polyethylene tapearticles having an average cross-sectional aspect ratio of at leastabout 10:1, said polyethylene having an intrinsic viscosity whenmeasured in decalin at 135° C. by ASTM D1601-99 of from about 7 dl/g to40 dl/g, and when measured by ASTM D882-09 at a 10 inch (25.4 cm) gaugelength and at an extension rate of 100%/min, said tape articles having atensile strength of at least about 2.2 GPa, said fabric being selectedfrom the group consisting of woven, knitted and three dimensionallywoven.
 3. An impact and penetration resistant assembly comprising atleast one member selected from the group consisting of a fabric asdescribed in claim
 2. 4. The assembly of claim 3 having an areal densityat least 1.5 Kg/m² and a specific energy absorption of at least 500J-m²/Kg at the V50 velocity as measured against a 9 by 19 mm FMJParabellum bullet by MIL.STD.662F.